1. Field of the Invention
The present invention relates to an intubation detection system, more particularly, to a transducer based intubation detection system with an indicator that indicates whether an endotracheal tube (or other tubular airway controlling device) is in a patient's esophagus or in the patient's trachea, immediately following an attempted intubation.
2. State of the Art
Endotracheal tubes may be used to pump oxygen enriched air into the lungs of a patient. The procedure is used in the operating room, the emergency department, and prehospital care settings, such as accident sites. One end of the endotracheal tube is connected to a source of oxygen and the other end is placed in the patient's trachea, in a procedure referred to as intubation. A danger in intubation is that the endotracheal tube may be placed in the esophagus rather than the trachea. Even an experienced clinician has difficulty in properly placing the endotracheal tube. Improper placement of the tube may result in permanent injury or death. Accordingly, detection of improper placement of the endotracheal tube is extremely important.
Clinical examination alone is dependent on the clinician's experience and judgement and may give misleading results. For this reason, accessory devices exist that help determine if the trachea is properly intubated. For example, capnographers have been used to detect improper placement. A capnographer is an expensive instrument that detects the presence of CO.sub.2. Confirmation of proper endotracheal tube placement is based on the fact that carbon dioxide is present in exhaled air in approximately 5% concentration, but is present in esophageal gas in only minute concentrations. The capnographer is a relatively large, sophisticated, and expensive reusable instrument that has a valid use in hospital operating rooms. The capnographer is too bulky, too expensive, and requires too much time to calibrate for routine use in prehospital settings and emergency departments. Unfortunately, it is these settings where experience may be limited and where esophageal intubations more frequently occur.
The EASY CAP End-Tidal CO.sub.2 detector is a currently available disposable device for use outside the operating room that assists in distinguishing esophageal from tracheal intubations by a color indication. The EASY CAP End-Tidal CO.sub.2 detector is marketed by Nellcor Inc. (formerly produced and distributed by FENEM Airway Management Systems under the name "FEF End-Tidal CO.sub.2 detector"). After intubation is performed, the CO.sub.2 detector device is attached to the endotracheal tube in line with the oxygen bag. Oxygen is insufflated through the device into the endotracheal tube and lungs, then exhaled back through the device. A change of color from purple to yellow with each breath indicates tracheal intubation. If the endotracheal tube is in the esophagus, no CO.sub.2 is detected and the color change does not occur.
The CO.sub.2 detector device will not easily detect tracheal intubation in the patient who is pulseless or inadequately perfusing the pulmonary circulation. This is due to inadequate CO.sub.2 exhalation. It will still detect esophageal intubation in these patients. However, many tracheal intubations will be interpreted as esophageal due to lack of color change. Clinical judgement is required in these cases.
Another technique for distinguishing esophageal from tracheal intubation is described in M. Y. K. Wee, "The oesophageal detector device assessment of a new method to distinguish oesophageal from tracheal intubation," Anaesthesia, 43:27-29 (1988). This technique relies on the relative rigidity of the tracheal wall, as compared to that of the esophagus. The trachea remains constantly patent due to C-shaped rings of cartilage supporting its lumen. The esophagus will collapse over the end of a rigid tube when significant negative pressure (with respect to atmospheric pressure) is applied in the tube, thus preventing aspiration of air. The more rigid trachea, on the other hand, remains open and allows free aspiration of air, when significant negative pressure is applied in the tube.
Under the technique, a detector device includes a syringe that is attached to an adaptor. After intubation, the adaptor is connected to the endotracheal tube. Air is aspirated into the syringe by pulling the syringe plunger. Free flow of air (i.e., ease in pulling the syringe plunger) is indicative of proper tube placement in the trachea. Resistance to flow (i.e., resistance to pulling the syringe plunger) indicates that the endotracheal tube may be improperly placed.